texts: How many arc seconds is Sirius "spiralling motion" around Sirius B?

texts: I know that Sirius A and B orbit each other. I'd like to ask how large is their relative apparent motion in arc seconds, seen from Earth?


texts: Why does Hellas Basin look white on some maps?

texts:
One map of Mars I see a lot is this colourized map: the Viking colourized global mosaic (Source):

But one thing which strikes me as odd is just how white the Hellas Basin is (the white patch which is not on the poles, just in the middle of the lower right half of the above image)
On the older version of the Viking mosaic, the basin doesn't look that white. Here the Mars Viking Colorized Global Mosaic v1
(Source, link to image):

It certainly still looks at least paler than the surrounding areas, but nowhere near as much as on the first map (on the first map it is about as white as the poles, on the second it is not).
So: Is the Hellas basin really as white as the first map suggests? And if yes why?


texts: Is the Apophis asteroid a concern for planet Earth?

texts: I was watching the TED lecture How to defend Earth from asteroids , and the speaker Phil Plait spoke of the possibility of this asteroid hitting Earth. Is this really a concern?


texts: How Soon Could a Waxing Crescent Moon Be Seen?

texts:
Question:

Apart from a Solar Eclipse, How much time is needed until a Waxing Crescent Moon be seen following a New Moon?

Would the time of year be significant? The Vernal Equinox + 1 Month.
Could it be seen the same night that it occurs?
Could it be seen in the day when it occurs?
Would this be affected if the viewer was in a rural location, without lights? Or would city lights help?

Context:
Ancient Lunar calendars depended on observation of the New Moon, (like political / religious obligations).
What was the potential margin of error? Hours? a Day? (Not considering bad-weather.)
From Wikipedia - A New Moon Cannot be Seen:

In astronomy, new moon is the first phase of the Moon, when it orbits as seen from the Earth, the moment when the Moon and the Sun have the same ecliptical longitude. The Moon is not visible at this time except when it is seen in silhouette during a solar eclipse when it is illuminated by earthshine.

Related:

Is it possible for a person to not see the new moon at different places on earth?
From which country or area is the new moon visible first?


texts: Would an object placed at L1 be seen in front of the Sun from Earth?

texts: Does anything placed at the Lagrangian point L1 between the Earth and Sun obscure the Sun like a transit of the innermore planets? The James Webb telescope is to be placed at L2, but if it was placed at L1, would it be in front of the Sun when looked upon from Earth? When you looked from the equator into the Sun, the telescope would be in the very center of the solar disc, right?


texts: Would space-based telescopes need to remain in the shadow of Earth to avoid light interference from the sun?

texts:
So I am thinking about orbiting telescopes tonight and I was thinking that it would probably be beneficial to keep them in the shadow of the Earth or some other space body to avoid light interference.

Specifically, I am thinking about looking off in all directions around Earth. I would imagine staying in a shadow would help the most. But that at the very least there would be a range of degrees around the direction of the sun that you could not observe until the Earth changed orbital position so that the Sun's light was no longer interfering when looking in a specific astronomical direction.

Am I correct in any of these assumptions? I believe there are telescopes that don't sit in the shadow of a body, but I do think that would greatly limit the range of area it could look at during a given timeframe.


texts:
I really want to know why I can’t see detail on planets.

This summer my Dad and I went on a trip to Utah I went outside to look at the planets and couldn’t see detail on Mars, Saturn, and Jupiter. Saturn's rings were visible but very faint and Jupiter was a white ball and then it’s four moons, this was all out in the middle of nowhere with 0 light pollution at 6000ft.

We then went into Bryce Canyon at 9100ft and still the same outcome the only difference was a very very faint strip on Jupiter, and it’s so dry in Utah and at an altitude of 9100ft where the atmosphere is not as heavy.

Is there still dew? Is my telescope not powerful enough I have an Astromaster 130 reflector and a 60az explorerscope refractor. I’m very confused


texts: Collimator for Dobsonian, same as Newtonian?

texts: I have been looking on line for Collimator for my Meade Dobsonian. The only Collimators I can find are made for Newtonian Lenses. It's a 8" mirror with a 1.25" lens. Will this work for my telescope?


texts: Could dark matter particles be unstable?

texts:
Is it possible that dark matter particles are unstable and the existing dark matter will decay in the long run and turn into hydrogen, for example? What would be possible mechanisms for such a decay?

Could some of the hydrogen we observe be "new" hydrogen, i.e. be the product of dark matter decay?


texts: Mathematical astrophysics subjects for math graduate students

texts:
I'm looking for a cool and interesting subject in mathematical astrophysics to study for my master's project. What I really aim for is certain processes in the cosmos (multiple body-problem, black holes, asteroid belts, colliding stellar objects, etc...), but my background is not very much on the physics side, unfortunately. However, I read about special relativity, gravitational waves and how to measure in space, but not in a very mathematical way.

I would like to hear from someone whether they know similar subjects like the above that are reachable for a graduate math student, like me, to study for their master's project.

My background is mainly in algebra (Galois, Geometry, crypto), but I also have done statistical data analysis courses and (P)DE courses; thus I have seen a rich part of mathematics, but my specialty is really in abstract algebra. However, especially now, I would like to get to know subjects that are not mainly abstract algebra, but more PDE, for example.

I'm ready to dive into depths of mathematical physics if necessary. Thanks for any suggestions!


texts: Which direction does the Earth face as it travels through the Galaxy

texts:
According to the Helical model, as the Sun orbits around the galaxy, the planets that orbit the sun are travelling perpendicular to the path of the Sun.  This is better shown in this video:

https://www.youtube.com/watch?v=0jHsq36_NTU

My question is, which pole on Earth faces in the direction that the Sun moves?  The South Pole or the North Pole?


texts: Would being ejected from the Milky Way Galaxy have any major impact on life on Earth?

texts:
I was reading about the impending collision of our galaxy with the Andromeda galaxy, and learned that there is a small possibility that our solar system could be ejected during the collision.

Assuming that orbits within our solar system remain unchanged (it is ejected as a whole), would floating in intergalactic space cause any significant changes in the living conditions on earth?


texts: What is a probability of a particle launched from earth hitting any object in the universe?

texts:
Imagine I pointed a laser into the night sky. How likely is it that a particular photon will ever hit anything?

This question bothered me for a while. I know very little about astronomy. When I asked my roommate he laughed and said that it must be very little, since the universe is mostly empty. I know it is true, but it seems to me that volume of the objects in the universe does not matter. Rather, it should be the area of objects when projected on a sphere that matters.

On one hand, universe is pretty empty, so hitting something outside the Solar System might be hard. But on the other hand, there are a lot of possible targets. These targets, however, appear smaller when the distance increases.

Which one of these, or other, forces will dominate? Would it make a difference if we ignored gravity?


texts: Objects entering or leaving the observable universe

texts:
Have there been any observations of objects entering or leaving the observable universe?

When looking at the physical limit of observing something like this I will to assume that the "object" would be an galaxy. I think it would be a good assumption to choose the size of such an galaxy, $G$, to be in the order of $10^{5}$ light years and the radius of the observable universe, $OU$, is $46 \times 10^{9}$ light years. Using the limit of angular resolution and the fact that the current biggest telescope has a diameter of 22.8 meters, then the longest wave length which would still yield would be about $40 \mu m$. When reversing the redshift, assuming this would be around $z=9$, then the longest emitted wave length which would be detected would be $4 \mu m$.

So observing such an event would technically be possible, however relative to the astronomical timescale we have only been able to observe with such a high resolution for a very short time, so the probability will not be very high.

And if such an event would be observed, would such an object suddenly appear/disappear. It will take along time for an entire galaxy due it size, so this would translate to more of a fade. Or will something else happen?


texts: Do/did the asteroids contain enough water to create Earth's oceans?

texts: It seems from the recent Science paper by Altwegg et al (2014) that the commonly accepted source of Earth's water being the comets might not be (completely) true. Their study suggest that the water in the comet they studied is different from Earth's (higher Deuterium content). The alternative source of water that Altwegg suggests is from asteroids. My perception is that there is not that much water in asteroids or at least not sufficient to create Earth's oceans. How much water is in asteroids now? How much water was there in asteroids reaching Earth when the oceans were formed?


texts: What would a terraformed Mars look like from Earth?

texts: Question in the title. Currently, Mars is a small orange dot in the sky. But what if green, blue, and some white were added? I wouldn't expect it to be too different- a large portion of it will remain pretty much the way it was, but with more snow (Tharsis bulge is REALLY high up).


texts: Why does the latitude of an observer affect the hour angle of a body in Stellarium?

texts:
I am using Stellarium for astronomical data to help in studying celestial navigation.
While trying to track down a source of errors in my sextant reading or sight reductions I noticed that the local hour angle (shown HA on Stellarium's ephemera) of Venus varied if I changed the latitude of my location whilst keeping time constant.

Can anyone explain this. I thought the HA would only be a function of time, longitude, and the position of Venus (RA, Dec). Why would my moving north along my meridian affect the HA of a body? Aren't both my meridian and Venus' fixed (time is stopped), so the angle between them wouldn't change?

I noticed that it changed systematically. For the date and meridian in  question (16/5/2020; 21:30:00 0° Long.) it varied from 6h 47m 41.86s at both the N and S poles, to 6h 47m 43.78s at the Equator. delta=1.92s

I know it's only a tiny amount, but I would like to understand what the principle behind it is. Everything I found on Google seemed to suggest it shouldn't change. I wondered if it was something to do with parallax changing as I changed position.

Thanks for any help.


texts: Identifying cataclysmic stellar phenomena

texts:
Cataclysms such as novas, kilonovas, supernova, magnetars, quasars, gamma ray bursts are rarely visible from Earth.   Under what conditions (such as distance, day vs. night, naked eye vs. level of optics) would such phenomena be visible from the Earth's surface, and what would they look like in terms of shape, initial duration, brightness, and so forth?

For instance, I have seen questions like how long does a supernova last and I have read that they can be visible for some time afterwards as a nebula forms, but this doesn't tell me what the initial burst would look like.  For instance, would it be possible to see a supernova in a neighboring galaxy such as Andromeda?  If so, how long would it be visible with the naked eye?  Would it look like a flash, last a few seconds, several?  I assume with a supernova not in our own galaxy there would be no subsequent light from the expanding shell since it would be too far away, whereas in our own galaxy if it were close enough we would subsequently see it, but in that case would there be a short burst of light, following by darkness and then the re-emergence of light, or would it be a continuously visible phenomena?


texts: How can red supergiants be cooler than dwarfs of the same spectral type?

texts:
The Stellar Classification Wikipedia article has a sentence:

Red supergiants are cooler and redder than dwarfs of the same spectral
type

Which seems to be true, my course has a similar statement. However, here is an HR diagram:

Spectral Class varies on the same axis as Temperature (see top horizontal axis). Does the claim that "red supergiants are cooler than dwarfs of the same spectral type" only says that since they are in the same spectral type, their temperature is roughly the same, but the red giant is a bit cooler, or is there more to the story and I am misusing the HR diagram?


texts: What are the prime challenges in search for extraterrestrial intelligence?

texts: What have we been able to accomplish so far and what are the prime obstacles that block our sight? My understanding is that Radio Telescopes are the prime tool for the search. I wonder what kind of challenges the astronomers who work on it are facing.


texts: I've seen something Incredible in the sky and really need help identifying what it is!

texts:
It was about 4 A.M. in North Wales and I was getting bored of what ever I was doing so decided to look out the window. I really love looking at the stars but this time it was different. The sky seemed to be a lot darker than usual which made the stars seem a lot brighter and, as you can imagine, I saw this one star which was slightly bigger than the other stars and it was in a triangular sort of shape; slowly moving, I disregarded it as a man-made object such as a plane of sorts but the more I looked the weirder it got, it had blue and red lights on it (really couldn't make it out if it was flashing or twinkling) and all off a sudden it changed direction and shot to one of the main stars in the sky and stayed there for about 5 minutes and then shot to another star and stayed there for another 10 mins, all of sudden really bright objects were shooting off the triangular star and going to other stars themselves as if they were all working as a team to cover the other stars in the sky, Then another 3 shot off the main one all 3 of them covered Orion's belt and so on with allot of other stars, I went back in because I thought I was loosing it, but called my mate to see and he had seen it too, but he's not as bothered as I was and just went back. The thing that made it even weirder was that where the big main star was there was millions of very faint brownish spots flying off it all around it.
Can someone please help and explain something to me because I need answers.


texts: Why are wavelengths shorter than visible light neglected by new telescopes?

texts:
The diagram below, which I stole from this post by @HDE226868, shows that angular resolution as a function of wavelength suddenly drops by three orders of magnitudes from visible to UV-light. The resolution of wavelengths shorter than what the Very Large Telescope Interferometer or the European Extremely Large Telescope detect, in the near UV, suddenly cuts off to a factor of a thousand.

This is obviously because of the properties of Earth's atmosphere. But major space telescopes like the JWST and WFIRST will fill in the far infrared gap. Why aren't there any as ambitious space telescopes planned for UV and shorter wavelengths? (Or is the sudden cut off in that diagram misleading?)

Is it because it is more difficult, even from in-space observatories, or is it because the angular resolution of UV and shorter wavelengths are of lesser scientific value?


texts: Q: Calculating the luminosity of a galaxy

texts:
I am currently working on a project on which I am calculating the luminosity of galaxies by using the SDSS data. They use a system of asinh magnitudes, and according to their website they use a system of softening parameters as it follows in https://www.sdss.org/dr12/algorithms/magnitudes/#asinh:

I used their cmodel magnitude that they advise for galaxies' photometry. For example, I have the r magnitude of this galaxy that is 14.68, and I am trying to find its luminosity. They say that to convert to flux density, one must follow the following equation:

S = 3631 Jy * f/f0, where for the r band the AB conversion and shift is minimal.

However, when I plug the numbers into the equation:

The distance of the galaxy is 63.3 Mpc
But it seems that when I plug the numbers, the final value does not match, how is that? And yes, I converted to the units including the Jansky to 10^-26 W m^-2 Hz^-1 and the Mpc to m.

I wish to find the luminosity of the galaxy in terms of solar luminosity and I know that one solar luminosity unit is the same as 3.827e+26 W.

I was only able to find the correct answer when I did the following equation:

Where:

If anyone knows what I am doing wrong point out, please. Is it because flux intensity is different from flux?


texts: How thick was Earth's primordial atmosphere?

texts: Earth's first atmosphere was made of hydrogen and helium accumulated before fusion started in the Sun. As soon as this happened it was stripped away by the Sun. How many atm of hydrogen and helium had Earth accumulated at the peak pressure of the first atmosphere?


texts: How to polar align an equatorial mounted telescope when you are close to the equator?

texts: I recently moved to southern Mexico (16 degrees N) and I wonder what would be the best way to align my EQ telescope when the polar star is not visible?


texts: Generate an uniform distribution on the sky

texts:
How to generate an uniform distribution of stars on the sky ? What I want is make a simulation of random points following uniform distribution on a part of the sky (making the assuption that we have the same amount of stars in any direction). The problem is how I do that because of the cos(dec) on the RA ?

What I did in python is this

import numpy as np
RA = np.random.uniform(-180,180)
Dec = np.random.uniform(-90,90)

But it is totally false, since we will have more points on the poles (if I do many points, this will clearly not be uniform)...

Thanks a lot in advance!


texts: What affects the evolution curve of a star's luminosity as a function of time?

texts:
Take a star of a given mass (say $1.0\ \mathrm{M_{\odot}}$ or $1.1\ \mathrm{M_{\odot}}$), what affects the star's luminosity as a function of time and how much? (metallicity?, rotation?)

It seems to me that stellar evolution is basically set by the laws of physics; if we know certain parameters (e.g., mass). Of course, that's the trick since we can't directly measure the mass of a star with no companion(s).

I have run across a few issues with published values being in conflict. For example, this study gives the age of Zeta Tucanae as being about $2.1-3.8\ \mathrm{Gyr}$. However, mass/radius/luminosity is given as 0.99/1.08/1.26 relative to sun (Wikipedia sources). If you look at an evolutionary plot of the Sun something is wrong here. (I'm guessing mass.) By the way [Fe/H] is given as -0.18.


texts: How does one find the electric conductivy of a planet's atmosphere?

texts:
I am working on an undergraduate project in which we study shaped structures in the atmosphere of the gas giants. We are investigating whether the magnetic field is the source of the instability generating the observed shaped structures. We therefore use spectral methods to make a stability study on the magnetohydrodynamics equations which in our case are

$$\frac{\partial{}\boldsymbol{B}}{\partial{}t}+\left(\boldsymbol{v}\cdot\boldsymbol\nabla\right)\boldsymbol{B}=\frac{1}{\mathrm{Re}_\eta}\boldsymbol\nabla^2\boldsymbol{B}+\left(\boldsymbol{B}\cdot\boldsymbol\nabla\right)\boldsymbol{v}$$

$$\frac{\partial{}\boldsymbol{v}}{\partial{}t}+\left(\boldsymbol{v}\cdot\boldsymbol\nabla\right)\boldsymbol{v}=\frac{1}{\mathrm{Re}}\boldsymbol\nabla^2\boldsymbol{v}+\boldsymbol{f-\nabla}p+\mathrm{N}\left(\boldsymbol{j\times{}B}\right)$$

where $\rm{}Re_\eta$ is the magnetic Reynolds number and $\rm{}N$ is the Stuart number expressed

$$ \mathrm{N} = \frac{\sigma B^2L_c}{\rho{}U}$$

where

$B$ is the magnetic field intensity;
$L_c$ is the characteristic length of the studied structure;
$\sigma$ is the flowing fluid electric conductivity;
$\rho$ is the fluid density;
and $U$ is the characteristic velocity scale of the flow.

Our model is now functional and the next step is to run the calculation with real values for physical parameters. We have all the data except the electric conductivity. Hence, I am  looking for this data (or a method to calculate an approximation). I thought that a first approximation could be made from the volume fraction of hydrogen and helium and their respective conductivity.

All ideas, avenues of research and scientific publication references are welcome. Thank you for help.

PS: I don't know much (yet) about astrophysics and the planet's atmosphere.


texts:
I'm currently developing a javascript application in which I want to calculate the approximate position of the sun. This works quite fine but requires the value for deltaT (TT-UT) to be set depending on the year for which I want to calculate the solar position.

Currently, I'm using a default value of 67 for my calculation. However, since I want to calculate the solar position for several years I'm looking for a convenient way to obtain the deltaT value for each year.

To all of you, that have some experience with programming:
Is there any interface (API) that provides me with the desired values?
Of course, it would also be sufficient to get the universal and terrestrial time so that I can calculate deltaT on my own.


texts: How can a low-mass star increase its mass to 1.4 Msun?

texts:
In my astronomy class I learned that a only low-mass stars (< 0.5 Msun) will contract, and then become degenerate, until it is a white dwarf. However, we also learned about the Chandrasekhar limit, which states white dwarfs have a maximum mass of 1.4 Msun.

If the starting star has less than 0.5 Msun, how does the resulting white-dwarf reach up to 1.4 Msun?

Am I perhaps wrong in my assumption that the mass of the resulting white-dwarf depends on the mass of the original star?


texts: I am very much interested in becoming an astronomer as a career. I know that my main focus should be in mathematics and science but; are there any specific degrees or competitive examinations I must obtain or attend, respectively? I am writing this question because I didn't obtain the desired answer.Please see my comment below for further information.


texts:
What elements are required to fuse into phosphorus in a star. Can someone give me a step by step process please e.g

  4 hydrogen nuclei fuse into one helium nuclei and then 3 helium nuclei
  fuse into carbon inside a red giant etc.

  1H x 4 = 1HE, 1HE x 3 = 1C etc.


texts: What do stars in galaxies without supermassive black holes revolve around?

texts: I still don't quite understand what the stars in galaxies without SBHs revolve around. I mean, the stars must orbit something. If the Sun suddenly disappeared, the planets wouldn't just continue in their orbits as there's nothing to orbit. E.g. M33 is thought to not have an SBH in its center. If the barycenter is in the very center of the galaxy wouldn't that require that all stars revolving around it have the same mass relative to their distance to each other, forming a gargantuan multiple-star-system? And how would such a system be stable over the course of thousands of years? Perhaps we are wrong and there is an SBH or another massive star at the center of each galaxy?


texts:
if I am not using very odd programming language for Astrophysicists, here is my code for calculating path of sun. I am following this reference

I want to calculate the local time as a function of zenith (e.g. sunset, sunrise, golden hour etc)

import java.time.LocalTime;
import java.util.Calendar;
import static java.lang.Math.acos;
import static java.lang.Math.cos;
import static java.lang.Math.sin;
import static java.lang.Math.tan;

/**
 * Created by rudra on 17/02/18.
 */

public class PathOfSun {

    static public double getTime() {
        LocalTime loacltime = LocalTime.now();//.getHour();
        double tzone = 5.5; //TODO: placeholder, will be calculated
        //    int localhour = time.getHour();
        int hour = loacltime.getHour();
        int min = loacltime.getMinute();
        int sec = loacltime.getSecond();
        double lat  =  28.6;//latlang.Lat;
        double lang =  77.2;//latlang.Lang;
        Calendar calendar = Calendar.getInstance();
        int dayofyear = calendar.get(Calendar.DAY_OF_YEAR);
        int daysthisyear = calendar.getActualMaximum(Calendar.DAY_OF_YEAR);
        double pi = Math.PI;

        double gamma = (2 * pi / daysthisyear) * (dayofyear - 1 + (hour - 12) / 24);
        double eqtime = 229.18 * (0.000075 + 0.001868 * cos(gamma) - 0.032077 * sin(gamma) -
                0.014615 * cos(2 * gamma) - 0.040849 * sin(2 *gamma));
        double decl = 0.006918 - 0.399912 * cos( (gamma)) + 0.070257 * sin( (gamma)) -
                0.006758 * cos(2 *  (gamma)) + 0.000907 * sin(2 *  (gamma)) -
                0.002697 * cos(3 *  (gamma)) + 0.00148 * sin(3 *  (gamma));
        double toffset = 4 * lang*60 + 60*(tzone) + eqtime;
        double tst = 60 * hour + min + sec / 60.0 + toffset;
        double ha = (tst/(4*60)) - 180;

        // Zenith
        double phi = acos(sin(Math.toRadians(lat)) * sin(decl) +
                      cos(Math.toRadians(lat)) * cos((decl)) * cos(Math.toRadians(ha*60)));
        // Azimuth
        double theta = pi - (acos((sin(Math.toRadians(lat)) * cos(phi) - sin(decl)) / (cos(Math.toRadians(lat)) * sin(phi))));

        // Calculating the hourAngle as in second page
        // At sunrise
        double ha2 = acos(cos(Math.toRadians(90.833))/cos( Math.toRadians(lat))*cos((decl))-
                tan(Math.toRadians(lat))*tan((decl)));

        double stime = (720 - 4*(lang + Math.toDegrees(ha)) - eqtime)/60.0;

        System.out.println("DayOfYear"+ dayofyear+ "  DaysThisYear"+daysthisyear);
        System.out.println("lat "+lat+"  lang "+lang+" ltime "+ loacltime);
        System.out.println("eqtime "+eqtime+"  ha "+ha+" , "+ Math.toRadians(ha)+ "  ha2 " + ha2+
                "\ndecl "+Math.toDegrees(decl)+" azimuth "+ Math.toDegrees(theta)+" Zenith "+Math.toDegrees(phi));
        System.out.println("Time of Sun "+ stime);

        return stime;
    }
}

The problem is its giving me more or less OK value for equationoftime and declination, but azimuth etc are grossly incorrect.

ANy idea where I am going wrong? I am following this page for reference.


texts:
Does a nova, not a supernova, get hot enough that nickel is produced despite its formation by fusion being an endothermic reaction? If nickel is made, does it make it out of the star into the nebula?

All I'm finding is this: Spectral Analysis of Central Stars of Planetary Nebulae which is not a very satisfying read.
I'd expect some nickel synthesis even in the core of non-nova stars. there's some equilibrium constant for the reaction after all, but it does not appear to be much talked about.


texts: What are the differences between TESS and PLATO exoplanet telescopes?

texts:
Within a year now it has been decided to launch TESS in 2017 and PLATO in 2024, space telecopes of NASA and ESA. They seem to have very similar science goals, both searching for transiting Earth sized planets in the HZ of the brighest (nearest) stars across all or most of the sky.

Are these missions as overlapping as they seem on first sight, or are there important complementarities? Is it perhaps the intention for PLATO to continue the observations of the planets discovered by TESS in order to get a longer time series?


texts: Why do scientists assume they can measure the shape of the universe if it is also widely believed to be infinite?

texts: The shape of the universe  is the question of whether the universe is flat, has a positive curvature or a negative one. More recently astronomers have compared radiation coming from extremely distant points of the observable universe and have concluded that it is flat with a 0.4% margin of error, Based on articles I've read elsewhere this seems to have created the consensus that the universe is indeed flat. But isn't the universe also believed to be infinite in size? If it is really infinite then shouldn't such measurements be inconsequential as an infinite curved universe would still appear perfectly flat to a local observer?


texts:
I'm doing a project for a statistics class, and I thought it may be interesting work with a dataset associated with astronomy. I know absolutely nothing about astronomy, unfortunately, and I wouldn't even know where to look for any large sets of data. Preferably I would want some data that could conform to a regression model, ie explanatory variables plus a response variable. Does anyone know of a place to look for what I am describing?

I know that the question is kind of general - I guess the important part is that the data is somewhat 'interesting' (something a layman understands), and that there are multiple variables that might possibly have a correlation.


texts: When will all eight planets in our solar system align?

texts:
Ignoring expansion of the universe, entropy, decaying orbits, and interference from any bodies colliding with or otherwise interfering with their orbits, will the eight planets known planets in our solar system ever align?

What is the "period" of the planets; how often would they align perfectly? And based on their current positions, how far off into the future is their next theoretical alignment?


texts: Why does Jupiter atmosphere does not get thinner on edges

texts: Looking at Jupiter image   the atmosphere edge of planet is very sharp as if it has solid surface which is not as it’s gases giant and there should be some thinning of atmosphere like we see around earth . Or there and could be seen on higher resolution images?


texts: Do Enceladus' geysers fall back to its surface or do they achieve escape velocity?

texts: Enceladus, a moon of Saturn, has a very low surface gravity at 0.114 m/s² or 0.012 g. It has a subsurface ocean of liquid water and is ejecting plumes of it. Does the ejected water eventually fall/rain down to the surface or does it (or some of it) achieve escape velocity due to Enceladus' very low mass and gravity? If so, is Enceladus losing mass and will eventually run out of water?


texts: How can the temperature of stars can be determined by their color?

texts: How do you determine the temperature of a star by color?


texts: What is the actual temperature of a quasar?

texts:
My daughter asked me last night: What is the hottest thing in the universe?

The first thing that sprang to mind was the core of a fresh neutron star (this question agrees: What is the hottest thing in the universe?), so I told her that and then tried to verify it on the Internet. Unfortunately, most of the articles online claimed that the hottest things in the universe are quasars, since they have a "brightness temperature" of 10 trillion kelvin. That sounded fishy, and a review of the literature revealed that brightness temperature has no direct relationship to actual temperature.

Poor journalistic practice aside, what is our best estimate of the temperature of these objects?


texts: Do we expect life to develop only in certain regions of the galaxy?

texts:
If I understand correctly, the Earth lies in an area of the galaxy - the "local bubble" - that is relatively free of dust and gases and where no new stars are being born.

What is the current theory on the relation between life on Earth and this location? Or in other words: Would we expect life to exist anywhere in the galaxy, e.g. also inside some nebula, or only in specific areas, and how are they characterised?


texts: calculating rising time from culmination time

texts:
I want to know how to calculate the rising time of a star, if
culmination and setting times are available with me?

Say Culmination time is 03:00 on 28-Nov-2018
and Setting time is 05:30 on 28-Nov-2018.


texts: Some stars such as a neutron star can spin very fast around 600 times a second, wouldn't the star be ripped apart? Although the gravitational pull is very strong but gravity is the weakest of all known forces and any good theory why neutron stars spin that fast does it have anything to do with the magnetic field and the surrounding dust clouds?


texts:
QUESTION:
Suppose we discover a planet orbiting a nearby star.
The distance to the star is 3 pc.
We observe the angular radius of the planet’s orbit to be 0.1 arc sec.
How many AU from the star is the planet?

**CONCERN: I am not sure what "The distance to the star is 3 pc" means. The earth's distance to the star? or the sun's distance to the star? or even better, the planet's distance to the star??!!

Any explanation of the question would be greatly appreciated!

My initial approach was some fixed position (say sun/earth's distance) to the star is 3pc,
so I will have    0.1 arc sec = 3pc/distance, and solve for distance as the answer.
(I reckon this is a very simple question for astrophysics, but I need to get basics right)


texts: Solar wind, Earth wind and planetary winds?

texts:
In February 2021, a new form of "electrified gas breeze" was announced, see blog by Tony Phillips entitled A New Form of Space Weather: Earth Wind which might a possible explanation for traces of water on the moon:

“Earth wind” comes from the axes of our planet. Every day, 24/7, fountains of gas shoot into space from the poles. The leakage is tiny compared to Earth’s total atmosphere, but it is enough to fill the magnetosphere with a riot of rapidly blowing charged particles. Ingredients include ionized hydrogen, helium, oxygen and nitrogen.
Once a month, the Moon gets hit by a blast of Earth wind. It happens around the time of the full Moon when Earth’s magnetic tail points like a shotgun toward the lunar disk.

I suspect, that all planets with atmospheres should display this kind of planetary winds (even without having a strong magnetic field), but I am sure it was never termed Venus wind or Jupiter wind since that naturally refers to processes within the atmosphere of the repsective planet. Does anybody know (publications) on the topic of gas jets errupting from solar planets with atmosphere? What order of magnitude would such a particle flow have for Venus or Jupiter?
References

H. Z. Wang et al.: Earth Wind as a Possible Exogenous Source of Lunar Surface Hydration 2021 ApJL 907 L32
Why did Venus not lose its atmosphere without a magnetic field?
Why has Venus's atmosphere not been stripped away by solar wind?


texts: Why does it make sense to say the universe has no centre?

texts: If we suppose we and everything in the universe is perfectly flat.  That is, we have width and depth, but no height.  And we are situated on the surface of a balloon blowing up with air and expanding "outwards".  Us flat people can move around on the surface of our balloon but not through it, in much the same way we navigate around the earth, in a plane say. No matter where something is situated on the surface of the balloon, one point is no more central than any other point.  In other words, the surface of a balloon (the "universe") has no centre.  Is this why we say it makes no sense to say the universe has a centre, or edge for that matter, or is this analogy stupid?


texts: Observation of Gravitional waves by LIGO from binary black hole merger

texts:
I read the paper "Observation of Gravitational Waves from a Binary Black Hole Merger"
https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.116.061102

I tried to understand all the graphs and data observed in the paper.
I am curious how these data and graphs conclude that the gravitational waves observed were because of binary black holes merger? Also what calculations and equations led to the same?
Also how will the calculations and equations look if neutron stars were there instead of black hole in the same merger?

(graphs and data can be seen in the observation section in the paper)


texts: How are younger objects outside our observable universe when the older CMB is an observer's temporal "edge"?

texts:
We know the observable universe is limited to objects whose light has had time to reach us and that an observer very far away will see a slightly different (assuming cosmological principle) observable universe with a slightly different (yet similar) CMB. We know that the CMB (cosmic microwave background or surface of last scattering) was released everywhere in the universe at once and is considered one of the earliest images of the universe. If objects (galaxies, stars et.) created after the CMB are outside our observable universe, why is the CMB our temporal edge? In other words, how are younger objects outside the older CMB? I understand that the universe is expanding, but wouldn't the CMB get redshifted then too?
edit:grammar


texts:
The rotation axis of the planet Uranus is tilted by 98° compared to its plane of orbit. This means that the north pole of Uranus is "under" the ecliptic compared to the north pole of other planets.

Why was the value of 98° chosen, rather than 82° ? How was it decided which pole should be north?


texts: How do scientists determine the age of stars?

texts:
I was Googling about the oldest galaxies in the Universe. Everywhere is written that their age is known by the light. Referring to this line "Since light travels at a set speed, if you look at a star ten light years away, you're really seeing what it looked like ten years ago" on this site.

So my question is, as we know light is continuous, how do scientists know that a particular ray has started its journey some 1000 light years back? How is the age of stars determined?


texts: A factor of cos(declination) in the formula of apparent of drift velocity of stars

texts: The angular drift velocity of stars is not the same for all stars and goes as $\frac{1}{\cos(\delta)}$. I don't understand why it should depend on the declination. All stars have to cover an angle of 360° in one sidereal day. Why should the angular velocity depend on the declination at all?


texts:
I would assume that, with light from more distant areas in space reaching the earth, we should be able to see more distant (and older) objects.
However there's lot of weird stuff regarding the space expansion that could eventually make the objects leaving us so fast the we'd never see them.

So, did we reach any boundary of what we can possibly see, or are we still working on more sensitive exploration devices?

I'll be grateful for some useful re-tag


texts: Converting equatorial coordinates to Cartesian coordinates for extragalactic distances

texts:
I'm trying to search for galaxy clusters with the friends-of-friends (FoF) algorithm. I have the equatorial coordinates ($\alpha, \delta$) and redshifts ($0.5<z<2.5$) of galaxies that I wish to convert to Cartesian coordinates, with the following:
$$
X = R\cdot \cos(\delta)\cos(\alpha) \\
Y = R\cdot \cos(\delta)\sin(\alpha) \\
Z = R\cdot \sin(\delta)
$$
The problem I'm having is deciding the correct $R$ to use: should it be comoving distance, angular diameter distance or luminosity distance, given that I only have redshifts to work with? How do we determine the best LOS distance measure to use for this case? Is there a better way to do this?
For example, in astropy, their default Distance quantity computes the distance from redshift (and a given cosmology) using luminosity distance.
References

Some notes on the Friends-of-Friends Algorithm


texts: How many days a month can you see a moonrise during daylight?

texts:
For about 15 days before a Full Moon the moon rises during the day, and for about 15 days after a Full Moon the moon sets during the day. I think it might be possible at full moon for the moon to rise just before daylight ends, and to set just after the next daylight starts, on some occasions.
However not all of these rises/sets will be visible. Around dark moon, moonrise is lost in the rising sun, and moonset is lost in the setting sun.
Hence my question, how many can you actually see?
I know this depends on a lot of factors, so a range would be sufficient.
I think this is equivalent to asking, what elongation of the moon is needed for the moon to be visible? When both are above the horizon?


texts: What does "Active Weather Patterns" mean?

texts:
I just read that Cassini discovered titan had "active Weather patterns".

What does that mean?


texts: "Radcliffe Wave" & filamentary dust structures

texts: A recent paper by Joao Alves et al describes a kpc-long dust filament with a long, thin dust structure with vertical sinusoidal wave component. From the limited art work that accompanies it, this structure appears to be one of those elongated filamentary dust clouds that lie on the interior shear surfaces of spiral waves and fore sides of galactic bars. Images of spiral galaxies with large scale arms reveal these dust filaments to be numerous and homomorphic. A number of studies, e.g. Hennebelle & Inutsuka and Gritschneder et al describe the properties of dust filaments in general. My question is whether kpc-scale elongated filaments along shear surfaces can in fact act as magnetic flux tube loci for multiple-generation GMC collapse into linear cluster complexes e.g. M16, M17, M8, etc. Can anyone recommend studies that address these issues?


texts: Is there sufficient evidence to confirm additional Planet in solar system

texts:
I have watched this scishow episode where Hank says that astronomers believe there is another planet in our solar system.

Link

He says that it's because how asteroids and comments are being pushed towards the sun (and us) from similar angles. Is this true? Do astronomers really have data that confirms the 'new ninth' planet?

EDIT: I did read the other related answers and articles, the way I understand this theory explained by tilt of 6 objects that could be explained by something massive enough pulling them. My question is do astronomers believe this is sufficient to confirm it that there is a planet.


texts: How Does Cosmology Constrain the Number of Neutrino Species?

texts:
I've asked this question already on the Physics SE, but I felt it would be worth posting here as well.

I know that based upon theories of structure formation cosmologists can constrain the sum of the masses of neutrinos - if neutrinos were too light or too heavy it would simply change the power spectrum of the universe.

My question is how exactly is the number of neutrino species constrained by cosmological measurements (i.e. - $N_{eff}$ as measured by WMAP or Planck)? The recent results from the Planck Satellite give us $3.3\pm0.3$, which is consistent with three neutrino species. How is this measured?


texts: Dotted line of moving objects observed on May 5th and May 12th

texts: I saw a dotted line shooting star-like object May 5th and May 12th. It was longer than any meteor/shooting star tail or trail I've ever seen before.  I mean longer in every way, the distance it traveled across the sky, the length of the dotted line and the amount of time I could see it.  I remember somebody from the UK asked the same question 9 months ago..


texts: Helium in terrestrial planet atmospheres?

texts:
When you look at effective temperature ranges and escape velocities of planets, there is a "population" where hydrogen escapes, but helium doesn't. Is it feasible that there may be planets less that about 10 Earth masses (not gas giants) with a predominantly helium atmosphere??

Another way of asking this question would be:
Do any models show terrestrial planets retaining a primordial atmosphere or is expected that most all will be secondary? I am guessing that very little helium is "outgassed", whereas hydrogen can be added to an atmosphere by photodissociation and other processes. I know that early star UV emissions, collisions, etc. will probably strip a "close in" planet's original atmospheres.


texts: Is it practical to build a giant telescope in Moon? (Considering the fact that the atmosphere of moon is very rare)

texts:
China's FAST (Five-hundred-meter Aperture Spherical radio Telescope) is the largest radio telescope in the world.(This is huge!!!)

As we all know Space Telescopes are better than Earth-Based telescopes always.(Hubble space telescope was such a tremendous success)Even though ground-based observatories are usually located in highly elevated areas with minimal light pollution, but still they contend with atmospheric turbulence, which limits the sharpness of images taken from this vantage point.

What if all the space agencies collaborate together to build a telescope half the size of China's FAST in moon(Even smaller than half),even then it will be more powerful than the "FAST" right(because the atmosphere of moon is very less dense)?Will it be impractical?It may take decades to build one but still the outcome will be huge(We may even look and find aliens!!)

(Taking in account that Elon Musk is already planning Colonization of Mars)This project looks somewhat tamable than that,right?  Is there a possibility of this happening? Is it feasible enough?


texts: If quasars are powered by black holes, why are they so bright?

texts:
If a black hole can swallow everything, even light, then how can a black hole power anything, particularly something as bright as a quasar. Why doesn't the black hole swallow the light of the quasar?

Are quasars formed when two black holes combine?

I assumed it might be like an orange when we press it from middle then its juice comes out from both ends.

Is my assumption right...or is there another reason?


texts: Which of Jupiter's moons did I most likely see?

texts:
I was gazing through my binoculars at Jupiter last night and noticed 3 (maybe 4) tiny dots in line with it. A first I thought they might have been background stars but quickly realised their colour was similar to that of Jupiter and their brightness was larger than expected considering their size. As a result, I'm pretty certain I was looking at Jupiter's moons.

Presumably, I was seeing the largest of its moons (Io, Europa, Ganymede, Callisto). They were far too tiny to see any details, obviously, but would it have been only those moons I could see? I assume the rest are too small. And is seeing those 4 moons as tiny bright dots through my 7x50s feasible?


texts: What is the term for a star swallowing another star?

texts:
A star A goes through the body of another star B, or is swallowed by B. There is no tidal disruption.

It sounds like kerzan. Does anybody recognise this pronunciation?


texts: Which Saturn satellite passes closest to Saturn's rings and at what distance?

texts: I was using Stellarium to watch Saturn from its moon Pan and I saw the rings were very close to this moon. Now Saturn's rings extend for a large distance so several moons see them from close. I was wondering, is it know which Saturn moon passes closest to Saturn's rings and at what distance?


texts: Why are these telescope mirror makers not upside down? (Daniel K. Inouye Solar Telescope)

texts:
The new open access Solar Physics article The Daniel K. Inouye Solar Telescope – Observatory Overview is the first of several papers about the new state-of-the-art solar observatory. For more info see Phys.org's Solar telescope releases first image of a sunspot
Figure 4 of the paper is shown below. It is the 4 meter primary mirror viewed at an oblique angle with several people in clean room garb standing behind it.
We can see their reflections in the mirror as well. The geometry is similar to people standing on the opposite side of a reflecting pool.
What struck me is that this differs in an important way; the people are not upside down!

Why not exactly?
Would the people see the camera upside down then?

It looks like the photo was taken from fairly close to the mirror based on the strong perspective scaling from foreground to background objects.

(Figure 4) The 4-meter primary mirror (M1) after coating at the AMOS coating facility on Haleakalā.


texts:
In school I learned that methane is organic matter and that it is a possible product of crude oil refinement. However, recently I read that Uranus has huge methane storms and the Saturn moon Titan even has lakes consisting only of methane or ethane.

Now, I'm wondering, how does all that methane get out there?

Is it the result of organic processes or is it created in the cores of suns like other elements? Do we even know?

Methane is also a pretty complex material. Do we know sources of more complex molecules other than methane in such quantities? Except life on earth?


texts: Does tidal locking also slowly reduce the orbiting body's axial angle?

texts:
The Moon is tidally locked to the Earth, and it has an axial angle of 6.687 degrees relative to its orbital plane. I'd like to know: did the Moon start out with a higher axial angle?
In other words, does the process of tidal locking also slowly reduce the orbiting body's angle of rotation? If so, how does this work? And will it someday cause the angle to be reduced to zero?
A secondary question would be: suppose an orbiting body had an extreme axial angle, say 80 degrees (perhaps due to an impact during its formation), how would this affect the process of tidal locking?


texts: Callisto's orbit: circular vs JPL is periodic 4 degree error, why?

texts:
I am approximating the azimuthal angle of Callisto from Jupiter or the Jupiter+moons barycenter using a constant angular speed circular orbit. This differs from the JPL ephemerides by only about 4 degrees, and the error has a very pleasant shape with a period of around 14 days.
However, none of the higher accuracy corrections I can find explain the 4 degree error (they seem to all be much less than a degree, and do not have the right time period). Is there a simple explanation?
I used a very simple formula:
angle = 21.57107 * time-in-days + angle-at-time-zero
This can be found from https://ssd.jpl.nasa.gov/?sat_elem or Meeus's Astronomical Algorithms (Chapter 43, satellites of Jupiter).
Meeus's book (I only have the first edition) list some corrections:

eccentricity
movement of the perijove (slow, less than 0.001 degrees per day)
a list of terms, the largest is 0.84 degrees, the rest 0.03 degrees and quickly decreasing in size

The eccentricity correction did not appear to help (it is listed with what appears to be an incorrect value of 21.487... instead of 21.57... but maybe this is my error). I used Kepler's equation (iterative solution, then cartesian form of ellipse, and arctan to return to the angle) to more directly handle the eccentricity, but Callisto's eccentricity of 0.0074 did not make much difference (the semi-major and semi-minor axis are the same length up to rounding on the JPL website).
Here is the graph of the error over about 60 (Earth) days time. Let me know if python code would make the question more precise. The JPL data is used to compute the position of Callisto with respect to the Jupiter system barycenter, and then I just take arctan2(y,x) to get the azimuthal angle. This agrees fairly well with the simple linear function angle = 21.57107*days, but with a +-4 degree variation depicted here:

Edit: I think I can explain away half (2 degrees worth) of the error by saying the orbit is tilted 25 degrees parallel to the equator. The reduced error still has a smooth periodic shape, but as far as I know, Callisto orbits around the equator of Jupiter. I checked that the JPL data does seem to include a 25 degree tilt.
I'm having a hard time interpreting things as my terrestrial mind has just started to grapple with the idea that a day (a full day-night cycle) is shorter near the poles of Jupiter than at the equator, and so what do we even mean by longitude. Does Jupiter have an equator? Does a barycenter have an equator? What is tilt?


texts: What is star composition after formation

texts:
Most descriptions of star ignition go something like... The star reaches a critical mass and ignites, blowing away the surrounding material. The most obvious question would be "Why are stars not all the same size?", given that the critical mass for ignition would appear to be the same, but I understand that stars can accumulate mass from collisions from other stars, planetary bodies etc.

So my question is also based on the fact that larger stars also burn more energetically, I assume blowing away more of the the lighter elements from the surrounding cloud after formation and gathering more heavy elements,... do larger stars have a significantly different composition from smaller stars? --- or is the simple description of star formation misleading?


texts:
So I tried deriving the radial co-moving coordinate formula to an observable galaxy for which the light observed at time  $t_o$ was emitted at time $t_{em}$. i.e  $r_0=\int_{t_{em}}^{to} c/a_{(t)} dt$

I tried deriving it without thinking about the Robertson-Walker metric, but with the relative velocity of light in space (the photon being like a boat on a water stream)

I think I might've made a conceptual error, and I hope that by posting my solution here someone will enlighten me.

In the above pictures $\tau$ is a chosen time with the property $t_o > \tau > t_{em}$; $v_{space}$ is the velocity of "space" (universe expansion) at the location of the photon (as you might've noticed, the relative velocity of the photon is given by the speed of light minus the speed of space); $r'$ is the "current" co-moving coordinate (at time $\tau$) while $r$ is the "old" (at emission) co-moving coordinate of the photon.

I'm sorry in advance if something is unclear. Feel free to ask for more clarification.


texts: What is considered "contact" for contact binary white dwarfs, and roughly how long can they stay that way before merging?

texts:
The question Why do they think that WDJ0551+4135 is “snowman shaped” i.e. a contact binary? has also raised the question of what a contact binary is or isn't, and how hard it might be to see one if it is, so let's explore this separately and then hopefully establish some usage guidance for the contact-binaries tag.

Questions:

What's considered "contact" in contact binary white dwarfs? Photosphere contact perhaps?
roughly speaking, how long can pairs like this stay in contact before merging? Millenia? Minutes? If the time is very short that means they are much harder to observe in a state of contact.

"bonus points:" Are there any contact binaries we can see by eye or with binoculars or a small telescope? (wouldn't have to be white dwarfs) Could we see one vary in brightness and/or color as the pair rotates?

From the BBC article cited in the linked question:

  Artwork: The object may be two so-called 'white dwarves' merging into a smaller denser star


texts:
When looking at a diagram of the optical path through a newtonian reflector, the lines always cross before the eyepiece. I understand that the eyepiece is used to focus this diverging light cone so that your eye can observe an image.

If you use a camera in "prime focus" i.e. Without an eyepiece to rectify this diverging light cone, it can discern an image anyway? Would this mean that the focus adjustment (distance from the focal point) merely determines the size of the image on the sensor? Or is there still a point where the image is in focus?

How do we ensure that this occurs while the light cone is still smaller than the sensor? Or is the whole image always varied in focus across the cone, just that the depth of field allows all of it to be in focus enough for a good image?


texts: Did I see a mentionable event in Germany early morning on 6th of February 2019?

texts:
Around 6.15am (GMT + 1) on the 6th of February 2019 I
was looking out of my window somewhat north, when I saw something one would probably call a shooting star. The features were:

A magnitude I haven't seen before; it even had a soft blinding effect, that's how bright it was.
From my view frame it moved from my right to my left (so most likely from east to west).
The size was a quarter to half of what the moon usually has from my view frame.
It traveled almost through the sky half I was able to see within half a second before its glow was immediately gone again.

I am assuming the object must have been either very large and fast or quite close.

Was there any meteor worthy mentioning passing by Earth at that given time?
Or are the features I just described way more common than I am assuming, and I just spotted an event that happens quite regularly?


texts:
After fooling around with a FITS file(s) (e.g. setting scale, changing color) is it possible to save the session such that there is a file associated with all those tweaks the next time I open it up?

Save and Save Image just seem to keep whatever I set it to, but when I load those new saved files back into ds9 the settings are all back to whatever default load settings I have enabled.

I would also like to be able to do this if I have FITS files loaded into multiple frames so I don't have to go through the process of loading each individual image.


texts: What can I see using a celestron nexstar 127SLT?

texts: I am planning to buy celestron nexstar 127SLT and I want to know what can I see using my telescope.


texts: Can life on earth be supported by only a Red Dwarf star or a White Dwarf(state still hot not cooled enough yet)?(Provided it is near to the star)

texts: Can a red dwarf star or a white dwarf have enough energy to support life on earth? How it will change the climate and the seasons of earth if it is our only star? (energy source)(Expecting it to change since earths orbital mechanics will also change)


texts: Will Earth rotate backwards in the future?

texts:
Hello recently I heave heard the earth will eventually start rotating in the opposite direction (ie sunrise from the west) . I am not sure if this is true, but a lot of sites are claiming it to be true, they say that the earth's rotation is slowing down slowly, and it will eventually stop and start rotating in the opposite direction, please let me know if this is true or not as I do not have much knowledge in astronomy.
EDIT:
Some of the sites that claim this event to be true, explain it in this way -
they say
"The earth is slowing down every year, so much so that when it first started spinning each day was only 4 hours but now it's 24 hours, a day will come when the earth will stop rotating and it will behave like a spring and then it will start rotating in the opposite direction (they don't mention if humans will be alive till that day or not) "
Here are the sources that led me to consider the possibility of this event-
1 - https://archive.siasat.com/news/nasa-confirms-possibility-sun-rising-west-102184/#:~:text=And%20this%20weird%20phenomena%20of,rise%20from%20the%20west!!
2 - https://medium.com/@loadjunker/nasa-confirms-possibility-of-sun-rising-from-the-west-ad5ddd166c11#:~:text=And%20this%20weird%20phenomena%20of,rise%20from%20the%20west!!
3 - https://www.express.co.uk/news/science/597607/Sunrise-WEST-Scientists-warn-magnetic-poles-SWITCHING-North-become-south
4 - https://medium.com/swlh/if-the-sun-rises-from-the-west-92452a570f86


texts: Is their any clue where gravitons come from?

texts: Everything which has mass has gravity. Some theories hypothesis that gravitons are responsible for that, but do they have any clue where they come from? Like gluons are interacting between quarks and photons between eg electrons. But does gravitons have, according to those theories, also have a kind of particle on their own with whom they are interacting with. Or is it possible that fe gravitons are also coming from quarks?


texts: Different full moon face on different places on Earth same time

texts:
I have theoretical question.
Let's assume that it is full moon and two different humans are looking at it at the same time. One human is for example in London and one in Beijing. It doesn't really matter where exactly, important is that they are almost on opposite side of Earth but they both see the moon at the same time.
I assume they see the moon from different angle. Is it possible that one of them see different part of the moon because of this angle. It could be just the border, tiny part.

Could you please tell me, how big is this tiny part of the moon which one see and the other don't? Few meters? Kilometers?

Thanks everyone for help.


texts:
GRAVITY (shown below) is a interferometric combiner of near infrared light from four very large telescopes called The Very Large Telescope in order to make careful astrometric measurements near the dusty galactic center where very exciting things happen near what we assume to be a supermassive black hole.
There have been publications of verification of general relativity by watching the star S2 pass through its periapsis around whatever the supermassive black hole-sized object is that it orbits. This was a major milestone in GRAVITY's contribution to science.

Is S2 still the fastest known star in the galaxy?

It may still be used for other things, but primarily...
Question: Was GRAVITY built to look at one star? Was the observation of S2 sufficient to justify this ESA effort? Or was it always also expected and required to do many more things?
From eso1825 — Science Release: First Successful Test of Einstein’s General Relativity Near Supermassive Black Hole; Culmination of 26 years of ESO observations of the heart of the Milky Way:

New infrared observations from the exquisitely sensitive GRAVITY [1], SINFONI and NACO instruments on ESO’s Very Large Telescope (VLT) have now allowed astronomers to follow one of these stars, called S2, as it passed very close to the black hole during May 2018. At the closest point this star was at a distance of less than 20 billion kilometres from the black hole and moving at a speed in excess of 25 million kilometres per hour — almost three percent of the speed of light [2].
The team compared the position and velocity measurements from GRAVITY and SINFONI respectively, along with previous observations of S2 using other instruments, with the predictions of Newtonian gravity, general relativity and other theories of gravity. The new results are inconsistent with Newtonian predictions and in excellent agreement with the predictions of general relativity.
[1] GRAVITY was developed by a collaboration consisting of the Max Planck Institute for Extraterrestrial Physics (Germany), LESIA of Paris Observatory–PSL / CNRS / Sorbonne Université / Univ. Paris Diderot and IPAG of Université Grenoble Alpes / CNRS (France), the Max Planck Institute for Astronomy (Germany), the University of Cologne (Germany), the CENTRA–Centro de Astrofisica e Gravitação (Portugal) and ESO.
[2] S2 orbits the black hole every 16 years in a highly eccentric orbit that brings it within twenty billion kilometres — 120 times the distance from Earth to the Sun, or about four times the distance from the Sun to Neptune — at its closest approach to the black hole. This distance corresponds to about 1500 times the Schwarzschild radius of the black hole itself.

Source

A new instrument called GRAVITY has been shipped to Chile and successfully assembled and tested at the Paranal Observatory. GRAVITY is a second generation instrument for the VLT Interferometer and will allow(s) the measurement of the positions and motions of astronomical objects on scales far smaller than is was currently previously possible. The picture shows the instrument under test at the Paranal Observatory in July 2015.


texts:
It is believed that our sun will become a red giant with a diameter of about 1 AU. When the fusion slows down, gravity will collapse the sun. Since the energy release from the fusion diminishes slowly (maybe hundreds of years for a significant change of 1%).

Let's assume that only a small fraction of the sun (10%) is needed to collapse (to 1/1000 the volume) to produce a nova. Would it still be possible for a star to collapse in a few hour (instead of decades)?


texts: How did the Hulse-Taylor Pulsar Provide Confirming Evidence of General Relativity?

texts: What measurements and observations of the Hulse-Taylor Pulsar agreed precisely with the predictions of general relativity, and how did these measurements support the theory?


texts: What are the exact physical parameters used to calculate Mercury precession with Einstein theory?

texts:
NASA measured 43,13 arc seconds per century. General relativity predicts 42,98 arc seconds per century.

I try to find out what the parameters' values such as $G$, $M_{sun}$, $\omega_{min}$ at aphelion radius, etc. used to get this exact 42,98.

With a new model developed by R. Plamondon, we get exactly 43,13 and also it matched perfectly with Mercury's period of revolution around Sun.

My problem is the following. When I put my parameters into Einstein metric, I got something unexpected.


texts: Sun's formation as "part of a star-forming-cluster..."?

texts:
After reading this interesting answer,

I was wondering, do we in fact know if our Sun in particular was created as part of a star-forming-cluster, or, was it more of a solo creation?

(Or, are all stars created as part of star-forming-clusters, is that the norm and how all stars come to be?)

If yes, indeed are we aware of which stars around us, are our sibling star?  (So, there's a list somewhere "stars known to likely be sibling to our Sun from a certain star-forming-cluster".)  Or have they dispersed over the 4 billion years and it's impossible to know, or is it just the case that "all the stars anywhere nearby" are/were indeed siblings from "our" star-forming-cluster?

Further, I'm having trouble grasping the order of magnitude of star-forming-clusters. Consider say "all the stars in our arm of the galaxy": Consider the question "in how many star-forming-clusters did all those stars originate?"  Is the answer like "3", "a few hundred" or "100 million" ??

Perhaps most simply: if sol formed as part of a star-forming-cluster, what's the order of magnitude of how many stars formed with it?


texts: Interpretation of Angular Correlation results

texts:
Long story short, what I am doing is to split the spherical space around my device into equal size pixels (49,152 pixels) with HealPix algorithm. If the power that my device can receive at each pixel is equal or higher than a certain threshold, I will color that pixel, if not, the pixel remains white. At the end, I want to find the angular correlations of the colored pixels (can be seen as galaxies). I started with the simplest estimator Davis & Peebles ($w(\theta) = DD/RR$) and it works fine. However what I achieve with LS estimator is hard to interpret since I get $w(\theta) = 1$ for large angular separations between my pixels (solid angle elements) which are separated around 170-180 degrees (I express it in degrees since I measure the arc length between 2 solid angle elements) apart and that is because I have no pairs in my DD and DR sets to be separated by 170-180 degrees. For instance:

$w(\theta) = (DD-2DR+RR)/RR$    --------->    $w(170) = (0-2\cdot0+RR)/RR = 1$

The question is what does this $w(\theta) = 1$ mean while I have no pairs in my data set separated by the mentioned large angles. In case if needed, attached is a set of plots to highlight the problem plus 2D representation of my data and random sets.

I would be greatly appreciated if you can help me how to interpret my angular correlation results from LS estimator.

Angular Correlation results for LS estimator and Peebles estimator:


texts: Why does each and every planet of our solar system have an unique axial tilt angle?

texts:
Why do planets have an axial tilt? From the above image we can see that each planet's axial tilt angle varies and differs from the others.

What was the cause of this, was this from the beginning of our solar systems birth? Or did it happen later?


texts: How to convert VSOP's xyz coordinates to heliocentric spherical lbr coordinates?

texts:
I ran VSOP2013 in Fortran, and I now have the following position $x, y, z$ as well as velocity $v_x, v_y, v_z$ data.

How do I convert the position to heliocentric ecliptic spherical coordinates $l, b, r$?

PLANETARY EPHEMERIS VSOP2013  EMB
Ecliptic   Heliocentric Coordinates:  X,Y,Z (au)  X',Y',Z' (au/d)  - Dynamical Frame J2000

Julian Day 2415021.0
-0.2054467990    0.9615310525    0.0002141233   -0.0171063024   -0.0036576954   -0.0000011815


texts: What does this information about "upper limit column densities" and "upper limit relative abundances" mean?

texts:
I was reading the abstract of a paper regarding attempts at detection of a molecular precursor to the amino acid glycine, and I came across concepts (and notation) that I found confusing. If someone could describe in layman's terms (I've taken an astrophysics class so I'm not totally unaware) that would be great.

In the question I refer to the following section of a paper's abstract:

  "we derive upper limit column densities of NH$_2$OH of $\leq 1.4 \times 10^{13} \mathrm{cm}^{-2}$
  and $\leq 1.5 \times 10^{13} \mathrm{cm}^{-2}$ toward the B1 and B2 shocks, respectively, and
  upper limit relative abundances of $N_\mathrm{NH_2OH}/N_\mathrm{H_2}$
  $\leq 1.4 \times 10^{-8}$ and $\leq 1.5 \times 10^{-8}$, respectively."

The paper in question is called CSO and CARMA Observations of L1157. I. A Deep Search for Hydroxylamine (NH$_2$OH), and located here.


texts: Question about semi-major axis mean separation

texts:
I am currently doing an assignment but I cannot for the life of me understand what one of terms used means. Notice I am not trying to get help with the assignment itself, but rather to make me understand so I can solve it.
Anyways, in the question (about visual binary stars) I am given their parallax angle etc etc, and I am to find the mass of them. But the sentence I cannot understand is the information given in "The semimajor axis (mean separation) is X.YZ'' and...(continue)", what does it mean? I draw two elliptic orbits and they intersect, I draw the semi-major axes of each ellipse. Is the semi major axis mean separation the angle that is between the semi major axes and the line drawn between each stars center in their elliptic orbits?
Help would be very nice. Thanks in advance!


texts: What is the accuracy of an artificial satellite at a certain magnitude?

texts: When we say that 'accuracy of gaia satellite is 10 $\mu$as at $V = 10$ magnitude in position and annual proper motion'. What does this mean? Does it change over time?


texts: Was Earth closer to Europa on 1983-11-25 or 1985-07-22?

texts:
xkcd #2003:

gives a humorous line of succession to the United States presidency. The comic's title text, found by hovering over the comic, states that a tie is broken by whoever was closest to the surface of Europa when they were born.

The only potential tie on the list occurs in item #19. It states the "champion" of the Nathan's Hot Dog Eating contest, but does not specify the men's or women's champion. At the time of the comic's publication, the men's champion was Joey Chestnut (born 1983-11-25) and the women's champion was Miki Sudo (Wikipedia gives only 1985 as her year of birth, but famousbirthdays.com claims July 22).

Both were ineligible to hold the presidency at the time of publication due to not meeting the minimum age requirement of 35. But supposing they both were, who would be first in line by the tiebreaker of distance from the surface of Europa at birth?


texts: Why is the main sequence often called 'zero age' main sequence?

texts:
The main sequence stage for a star begins after it stars burning hydrogen into helium. This is often referred to as the zero age main sequence.

This is confusing since stars have already lived several million years in their pre-main sequence stage.

Where does this come from? Is it a historical designation that just stuck?


texts: Astronomical databases for machine learning?

texts:
I was reading this question about open problems in astronomy. The bounty-receiving answer says that

  I have just left the field where some colleagues are trying to develop some software to use image subtraction techniques to isolate individual stars in the centre of clusters.

I find this problem interesting. Where could I find databases of astronomical images for testing different kind of ML techniques to solve such problems?


texts: In SETI has anyone calculated an estimate of the mean time between observations?

texts:
So the Drake Equation, proposed by Frank Drake, is often cited as a means to estimate the number of intelligent civilizations that exist in the observable universe.

Initial calculations by Drake came up with a number of about 10,000 civilizations. But refinements in the equation on how to interpret, and updated data, have recently led to this evaluation published in Astrobiology Magazine:    "There is a 75% chance we could find ET between 1,361 and 3,979 light-years away"

But what I'm more interested in has to do with our technology and efforts in detecting the first civilization in terms of estimating a mean time between observations.

Surely given the result of the Drake equation, our current efforts, and possibly other factors to consider such as sampling theory there must be a way to calculate this. Has anyone pursued this? If so what are the results? hours?, days? years? centuries?

Such a calculation I believe would justify more concerted efforts and investment or otherwise abandonment of any hope. Or perhaps a different strategy to mitigate the assumptions on the calculation to reduce the mean time.


texts: Initially non-flat space-time makes dark matter obsolete$\dots$

texts:
After the Big Bang, dark matter clusters and build the seeds for visible matter, that then forms stars, planet, you, me, everybody...

But do we really need dark matter to build cluster first. What if spacetime isn't flat per se on cosmlogical sclaes but rather crumbled or heterogenous, like a 4-dimensional version of folded cloth. We don't need dark matter, if we accept that space time didn't came along at the big bang in a clean way, as mathematical text books on general relavity suggest.

Is it possible to support this idea with astronomical data of galaxy mergers?


texts: Why is rotational motion absolute, is the universe spinning?

texts:
When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say it is the observer that moves at 1/4c and the object is stationary relative to it. It has no internal acceleration.

Experimentation at small scale will tell that a spinning object displays increasing internal acceleration the further away from its center of mass it is measured. -centrifugal force-

This forbids rotational motion to be understood as something relative, in the same way as uniform rectilinear motion is, so that when an object spins around its center of mass, noone could say "No, this object is rotationally stable, it's the entire universe that spins around it."

Fundamentally, why and how is rotational motion absolute in this way, and how could we know if the universe is or is not spinning at larger scale, at some spinning rate we cannot measure since we're trapped in this spinning reference frame, unable to detect it experimentally since it's too huge?


texts:
How could the lunar eclipse of January 20, 2019 begin from bottom to top and then finish from left to right?  Here's the video of it's progression's directions.
https://www.youtube.com/watch?v=A2sTkuZht4s


texts:
We have discovered some incredibly massive stars. R136a1, the most massive known star is estimated to have 265 times mass as our Sun. Yet it has been burning for at least a million years, and must have shed a considerable mass as stellar wind. In its infancy, R136a1 must have been much more massive.

Which got me thinking about the question: What is the theoretical limit of mass that a newborn star can have?


texts: As we know magnetars have strong magnetic field but what if we swap earth with a magnetar and the sun will released a solar wind. Is the magnetar affected by the solar wind or not ?


texts:
Where do asteroids impact upon the Earth most often?

Are impact zones primarily along the equator?

Is there an average area where impacts are more likely to occur?

If there is a zone, is there a way to determine if it's changed? More to the point, if there is an impact zone, are there any similar areas that might indicate the zone has shifted?


texts: If the hypothetical planet beyond the Kuiper belt exists, is it likely there are even more planets farther outside?

texts:
Since 2016 there are hints that a (probably) ice giant planet may exist far beyond the Kuiper belt. There are speculations that it may be a rogue planet captured by the Sun. But is it likely that there are even more undiscovered planets farther beyond, which also may be captured rogue planets or something?

I must clarify that the planet may be no captured rogue planet, it could also be a planet that was pushed into the outer system by the gas giants or so.


texts: How to calculate a meteor's entrance altitude to Earth's atmosphere?

texts: Also, in which altitude did fireball went thermal explosion?


texts:
This article Mars atmosphere states that

  Today Mars atmosphere is very thin, but it was not always like this. Around 3.5 billion years ago, the red planet had a thick enough atmosphere for liquid water to run smoothly on its surface

Suppose you could increase Mars atmosphere volume by melting frozen CO2 or whatever. How much volume of gases could be added to Mars atmosphere that the planet gravity can retain?


texts:
A gamma ray burst produces somewhere around 1044 J of energy, according to Wikipedia. Only a small portion of that energy will be absorbed by other objects.

The rest of that energy will go on to travel the universe indefinitely I presume?

How do we know how much of the universes total mass-energy is in "in transit" in the form of gamma rays and other forms of radiation?


texts: I was studying our solar system and all celestial objects are depicted as round objects, including black holes.. worm holes as hollow cylinders as a pathway across two universes.. even the galaxy is show circular.. Why does this happen?


texts: What is meant by *topocentric* right ascension and declination?

texts:
I'm looking up how to convert an azimuth/elevation measurement from a specific location on Earth's surface to right ascension/declination.  I'm coming across the terms "topocentric declination" and "topocentric right ascension", which I haven't come across before.

What does the "topocentric" mean here? Is this different from "regular" RA and dec?

My guess from the terminology is that, for objects that can't be treated as being infinitely far away from Earth, "topocentric" is used to differentiate a sky position of an object as seen from a specific place on Earth instead of from Earth's center.  (For very distant objects, like stars, the sky position seen from Earth's surface and Earth's center are for virtually all purposes going to be the same.)

If my guess is correct, is there a convention specifying which equator and equinox the topocentric RA and declination use?  Is it supposed to always be true equator and true equinox, or something more along the lines of a J2000 epoch?


texts: Planets form from disks of matter orbiting around a star; some moons form from disks of matter orbiting planets. If this were going to happen around Saturn, approximately how much time would it take?


texts:
Based on this answer, I should be able to figure out this question, if I know the distance between Betelgeuse and its nearest neighbor. So what is Betelgeuse's nearest neighbor?

I do mean the nearest neighbor in 3D space, not in the plane of the sky. Since Betelgeuse is fairly close to the Sun, I'm guessing we should know its neighborhood with a pretty good precision.


texts: How would parallax affect an object at 200-1000 AU (for example, the 9th planet)?

texts: We know from this question that an object is hypothesized to be at between 200-1000 AU that is large enough to detect, known now as the 9th planet. It should move about 40 arcseconds per year. It seems to me that the parallax distance would be more than this distance per year. Would it be easier to detect the 9th planet using parallax than its movement around the Sun?


texts: How to check what telescopes were looking at a certain portion of sky at a particular time?

texts:
I have some data that I collected from observations at a specific RA, DEC and I am trying to figure out what telescope surveys were looking at that portion of the sky at that particular time? I am currently trying to use NAVO's python notebooks to query databases but I'm struggling.

Any help would be greatly appreciated!


texts: How can I use Polar Alignment to find objects in the sky?

texts: I have a six inch telescope on an equatorial mount and I've been struggling to use the mount properly. For a couple months now, the only strategy I've used is just 'point and look.' I've watched some youtube videos on polar aligning a telescope, but none of the videos ever tell me how I can use polar alignment to find other objects after I've aligned. Is polar alignment even the right method of finding objects? If so, how can I use the degrees and minutes on my RA and DEC knobs to point directly at an object?


texts:
The BBC article Event Horizon Telescope ready to image black hole describes the Event Horizon Telescope, a coordinated observing technique with several radio telescope arrays across the globe forming a synthetic aperture with an Earth-sized baseline.

$$\frac{\lambda}{r_{Earth}} \sim \frac{r_{Sag A*}}{D_{Sag A*}} \sim  10^{-11}$$

...when plugging in 1 millimeter for $\lambda$, and with $r_{Sag A*}$ and $D_{Sag A*}$ the radius of, and distance from Earth to Sagittarius A*, the black hole in the center of the Milky Way Galaxy of 20 million km and 26,000 light years, respectively. (values taken from the article).

The equation I've written shows that millimeter wavelength interferometry with an Earth-sized baseline has the possibility to resolve the existence of some structure with scale of the black hole's event horizon.

My question is How does the Event Horizon Telescope implement the interferometry? It would certainly be impossible to bring all signals together to a central site and perform the interference there in real time as down-converted analog signals, and quite difficult/expensive to do it with dedicated, synchronized digital optical fiber lines. Is the massive amounts of data sent as IP packets over the internet to a central correlator (numerical interferometer)?

The article mentions atomic clocks and lots of hard drives, and I have a hunch these have something to do with it.

above: "The eventual EHT array will have 12 widely spaced participating radio facilities". From BBC.


texts: If the Wow! signal was not directed at us, then where?

texts:
We probably all know the Wow!-Signal, happened on August 15, 1977. Assume that it wasn't meant for us. What was it pointing at then?

The signal at that time came from RA= 19h25m31s ± 10s or 19h28m22s ± 10s and the declination becomes −26°57′ ± 20′.

Which stars could it point at and did anybody investigate this?


texts: How big are the rocky/icy cores of Jovian planets?

texts:
The size of Earth? Or bigger? I'd think they'd have to be pretty big to attract all that gas when the planets were being formed.

edit I'm writing a short story and the setting consists of late eighties/early nineties type of technology and knowledge of astronomy, so a rough estimate as an answer is fine


texts: Under what situations can an aperture mask improve the resolution of a small/medium amateur telescope? Is this demonstrable mathematically?

texts:
@antlersoft's answer describes some of the challenges to seeing any details in the small disk of Mars in small amateur telescopes. In the case of reflecting telescopes, it mentions the use of either an off-axis parabolic mirror, or an off-axis aperture mask on a standard Newtonian to produce a clear unobstructed view.

The answer links to a short article on the amateur telescope site BBAstroDesigns which is titled Off-Axis Masks: Light Reduction and Resolution

If I understand the explanation correctly, besides the light reduction function, the off-axis masking excludes the secondary mirror and support, thereby removing diffracted light.

I'm a bit surprised that for amateur viewing on Earth that diffraction from a Newtonian or Cassegrain's secondary mirror and supports would really have any impact on resolution of small extended objects like Mars. The example in the article is a 16 inch telescope. I would have thought that seeing would be the limitation, but maybe for bright objects a smaller diameter (1/3 to 1/6 of the full aperture) is actually better?

Is it possible to explain the physics/optic behind the use of off-axis apertures to improve resolution as discussed in these links?

If possible, can a bit of math be used to demonstrate this quantitatively and convincingly?


texts: When a star system forms from a cloud of gas and dust, why doesn't the dust migrate towards the centre of gravity with the gas to form a star? Why does dust in the accretion disk aggregate to form rocky planets, rather than fall into the proto-star?


texts: Instrument aperture sizes on Hubble Telescope

texts:
When looking at the diagram of the focal plane of the Hubble Space Telescope I noticed that the aperture sizes of most of the scientific instruments are very small. They occupy a very tiny fraction of the focal plane.

I understand that for a spectrograph (like the COS) you need a very small aperture to look at point sources. But why the Advanced Cmaera for Surveys or Wide Field Camera 3 also have so small apertures? Most of the focal plane is not used and it must be very tedious for the guidance system to move the target object exactly into the small aperture of the selected instrument. Even though the WFC3 is called "wide field", its field of view is less than 3 arc minutes.

What were the reasons behind selecting these aperture sizes? Is HST designed to observe details of small targets? Are the sizes optimized for majority of observations?

On the other hand the HST is taking images of large objects like nebulae and usually it is necessary to stitch a number of individual frames to create the whole image of a bigger object. For example the Carina nebula (stitched from 48 frames) or the Crab nebula (24 frames).


texts: How do we know or predict which particles were present before Big Bang Nucleosynthesis occurred?

texts: I'm reading Carroll and Ostlie's "An Introduction to Modern Astrophysics". In the BBN section, they describe that the universe contains a mixture of photons, electron-positron pairs, and electron and muon neutrinos and their antiparticles. They also mention that there was a small number of protons and neutrons and that protons and neutrons were constantly being transformed into each other from various reactions. From my understanding (not C & O necessarily), the Heisenberg Uncertainty Principle permits matter to spontaneously appear because there is some uncertainty as to how much mass there is in a vacuum; however, these particles must appear in "pairs" (ie. positron and an electron). If we assume inflation is correct, it is thought that these particles would become diluted after this process. So I guess I'm wondering how are these particles predicted in general (during the radiation era)? Is the energy released during inflation thought to have created these particles or something else?


texts: What was James Bradley's calculation to calculate the speed of light?

texts:
Looking into the history of how the speed of light came to be determined, to what we know it to be today, James Bradley is often mentioned. He was credited with the discovery of the aberration of light and having used the aberration of light to calculate the speed of light. There are many online sources that confirm this, though the year of discovery and calculated speed of light differs here and there.

I've read through Bradley's "A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and F.R.S. to Dr.Edmond Halley Astronom. Reg. &c. Giving an Account of a New Discovered Motion of the Fix'd Stars" published in "Philisophical Transaction vol 35" which explains his findings of the aberration of light but makes no mention of calculating the speed of light.

How did James Bradley calculate the speed of light and what publication of his shows these calculation?


texts: Does cosmological horizon grow or decrease as it radiates?

texts:
Black holes decrease as they evaporate and their radius decreases as well.

So what is with a cosmological horizon?

If cosmological horizon is just a black hole centered at the opposite side of the universe, we should see the radius of the external space groving as the radius of the BH decreases.

But if the radiation decreases the horizon entropy we should see the area of the horizon decreasing.

What is the correct conclusion?


texts: Why is the Earth called terrestrial? Can we call the Earth an ocean planet?

texts: Why is Earth called a terrestrial planet even though it is 70% covered by water?


texts: Could a spectrometer on a probe or space telescope identify minerals, not only elements and molecules, from the spectral lines? Is there any technology for identifying minerals remotely?


texts: Which side of earth will face toward sun when earth and sun will be get closer and be bonded by Gravitational Force?

texts: We all know that one day the distance between the Earth and the sun will be zero. They will be bonded with gravity. My Question is which side of the earth will face toward the sun? I can't calculate that. Someone please calculate and don't say it's impossible.


texts:
I was looking for accurate and up-to-date data regarding the advancement of the perihelion of the planets in the Solar System, the only ones I've found so far are at least 90 years old bout I really doubt that no progress has been made so far in this field... does anyone know where to find newer ones?

In addition to this, can anybody make an estimation about the difference between the Moon-Earth system precession around the Sun and a Moonless Earth system? It should be very small, too small to be detected maybe...

Thank you in advance!


texts: Can looking at the sun through solar viewing eclipse shades everyday harm your eyes?

texts: I have a pair of Solar Viewing Eclipse Shades that say "Safe for Direct Solar Viewing" and would like to know if my eyes would be harmed if I looked at the sun everyday for about a minute wearing them.


texts: Is it possible for a star to orbit a planet?

texts:
Is it possible for a red dwarf to orbit a gas giant?

OR

Has this happened and it is just assumed that the gas giant is orbiting the star?


texts: How do they keep lights from guided lasers in adaptive optics from interfering with the image?

texts:
From amateur searching of the info, I can find no mention of the configuration of the lasers when they work. From these pictures, I imagine that those 4 lasers are just outside of the 4 corners of the telescope field of view. Since the lasers leave such strong reflections on the equipment, how do they keep those lights from messing with the result images? Also I think the artificial stars may somehow affect the final picture too, even if they're not in the FoV, simply because they're so bright.
Maybe the scientists do it by simply filtering out the wavelength of the laser in their results? But that way they won't be able to see any sodium lights in the faraway stars, either.


texts: visualisation of the universe's expansion

texts: in physics we were learning about the universe and the big bang. we were being told that everything came from one point and 'exploded' outwards, and is continuing to expand. I felt that this explanation was unclear, so I said that it was more like everything being one the surface of an expanding 'balloon', but with an extra dimension, a space which is the hyper surface of the expanding universe. my teacher disagreed and said it was just like a big explosion. I think this is wrong-it implies that there is an edge of some description, or that the universe is just an expanding sphere of stuff inside infinite space. what is the best way to visualise the universe?


texts: What telescopes have observed anomalies in the light curve of Tabby's star, KIC 8462852?

texts:
KIC 8462852, the F-star that inexplicably dims by up to 20% for short periods, is still getting alot of attention. A slow continuous dimming by about 0.3% a year has been identified recently. But all anomalies I know of come from the Kepler space telescope. It is an F3-star at 1500 ly distance. Shouldn't it be easy to observe its light curve with even relatively modestly sized ground based telescopes? Have such observations been done and have they confirmed any anomalies? You see, I suspect something weird went wrong with the Kepler telescope here.

EDIT: There have been studies of its brightness on archived historic photographs. But I'm more interested in observations simultaneous as Kepler or since then, to confirm either a gradual dimming or short deep dips.


texts: How is the diameter of a gas giant calculated?

texts:
As we know atmospheres of celestial bodies don't just stop at a given distance. They gradually become less dense as you move away from the center.

I understand that the diameter of stars is typically given to be that of their photosphere (i.e. the boundary where a laser shined from behind the star toward an observer would just barely be visable).

I assumed that a similar method using optical depth also applied to gas giants. However wikipedia currently has the somewhat confusing explanation:

  As Jupiter has no surface, the base of its atmosphere is usually
  considered to be the point at which atmospheric pressure is equal to 1
  MPa (10 bar), or ten times surface pressure on Earth.

Which isn't quite the same thing as diameter, but it got me thinking: When wikipedia or a textbook or whatever lists a diameter for a gas giant how is that figure arrived at?


texts: Why can't the surfaces of stars be observed?

texts:
If I'm correctly informed, only three stars: Sol, Betelgeuse and Altair have surfaces which have been resolved by telescopes. All other stars are only point sources of light, even in the greatest of telescopes. Is it just the huge distance to the stars which reduce them to dots? Or is there some other optical explanation? I mean, the Sun is about as large as the Moon on the sky, but I cannot see any details on its surface because it blinds me. However, the next nearest star is invisible to the naked eye.

Some exoplanets have been directly imaged by removing the light from their star. It seems funny that we cannot detect any features on the photosphere of such a star, such as spots or flares or its shape. Plenty of photons are available.

Actually, there are several stars which have been directly imaged, maybe my sopposition is quite wrong:
https://en.wikipedia.org/wiki/List_of_stars_with_resolved_images


texts: When the Moon formed and early on, did it orbit over the Earth's equator?

texts:
Or was it always at about 5.14 degrees inclination or has the inclination changed over time?

See diagram.

James K's answer to this question got me thinking about this, and I don't mean to call him out, but this part of his answer doesn't seem quite right when he wrote:

  Our moon is unique in being close to the plane of the ecliptic, and
  not in the plane of the equator, which suggests its formation was not
  like that of other moons in the solar system.

For starters, I imagine the physics of the initial orbit of an impact moon would be somewhat complicated, but it seems likely, given an angled impact like the one that's believed to have formed our moon (and hitting at an angle is statistically more common than a direct impact anyway),

So, in this scenario, the planet gets significant angular momentum and this angular momentum should dictate the planet's new equator and axial tilt relative to it's orbit.  I would think the moon should form roughly along that same equatorial plane, but I'm just guessing.   Perhaps it could form several degrees off - not sure.

The 2nd point, is, a rapidly rotating planet with a large equatorial bulge and a close moon, if the Moon formed off the equator, would it's orbit migrate over the equator where the gravitation was greatest and would that happen relatively quickly or not at all?

That's basically the question.   Was the Moon always at roughly 6 degrees off the Earth's equator or has it only moved off an orbit over Earth's equator more recently, perhaps due to the gravitational effect of the Sun?

Or are there other factors.   Mars' axis is thought to have changed rather significantly due to Jupiter's gravitational effects perhaps 100,000 years agao and it's Moons orbit over Mars' equator which suggests that Mars' equatorial bulge dragged the Moons with it? - or is my thinking way off on that?

My thinking is that a planet's equatorial bulge would drive moons towards a 0 degree inclination around it's equatorial bulge and our Moon is different because of proximity to the sun which also has a strong gravitational effect.   The 5.14 degrees of inclination is a balance between the Earth's equator and the solar gravity.


texts: The name of a particular low extinction region

texts:
There is a region called Baade's window.

I remember there is a similar region called "somebody's window", which also has a low amount of dust.

Does anyone know the name?


texts: I would like to calculate the angle formed by the sun and the horizon for any hour of the day and any day of the year for a particular place on Earth.  So like: what is the angle of the sun to the horizon at 11AM on June 21 at Chicago?  (Sorry, I'm a newbie, and don't even know what the name of this angle is).  Is there a formula for calculating this?  Thanks!


texts: How does large body gravity affect planet formation?

texts: If Jupiter's gravity is what kept the asteroid belt from forming a planet, then why didn't the sun's gravity keep the inner planets from forming?